We are studying the ultrastructure and histochemical characteristics of various cellular and structural elements of bone marrow and spleen in normal state and in various hematological diseases with special attention to histopathogenesis of splenic lesions in Hodgkin's disease and non-Hodgkin's lymphomas. We are investigating the mechanisms that control the delivery of mature cells from the hemopoietic compartment of the bone marrow into the circulation. This is done by studying the ultrastructure of bone marrow sinuses in phenylhydrazine-induced hemolytic anemia, after blood letting and following intravenous injection of quartz particles. In the latter situation the control mechanism sustains injury resulting in the appearance of immature cells into circulation. We are investigating the lipid biochemical composition of marrow adipose cells. We shall study this, in red marrow as compared to fatty marrow. We shall further compare the lipid composition of red marrow in normal state and in aplastic anemias. Preliminary results using lipid histochemistry indicates that the lipid composition of marrow may be related to the hemopoietic function of this tissue.